1. Field of the Invention
This invention pertains to a hydraulic control system for an automatic transmission and more particularly to such a system, which upon sensing an unacceptable combination of pressurized clutches and servos reverts to the combination that produces a predetermined speed ratio.
2. Description of the Prior Art
Automatic transmissions for automotive use include planetary gearsets, whose elements are hydraulically engaged or braked in order to produce selected speed ratios between the engine crankshaft and the output shaft of the transmission. Automatic gear change transmissions may be controlled by electronic means which produce digital voltage signals that are converted to analog signals to operate solenoid valves. These valves connect hydraulic line pressure to the selected clutches and brakes or vent the hydraulic cylinder of these elements to atmosphere. The control system should operate such that in the event of a control system failure the transmission may operate in at least one forward drive range and in the reverse drive range in order to permit driving the vehicle to a service or repair station.